Polymer dispersed liquid crystals (PDLCs) typically are made by inducing phase separation in an initially homogeneous mixture of liquid crystal and monomers. Preparation of PDLCs involves a phase separation, which is conventionally triggered by polymerization of the monomer matrix by either UV or thermal curing, or even rapid evaporation of solvents. As the monomer polymerizes, the liquid crystal phase separates into microscopic droplets or domains or pockets surrounded by the walls of the cured polymer matrix, which provides a “backbone” to hold the LC. The mixture of cured polymer and LC are held together between two sheets of polyethylene (PET), often coated with transparent conducting oxides (TCOs) through which an electric field is applied. When unaddressed (e.g., when no voltage is applied), the nematic texture within the domains is randomly oriented with respect to the other neighboring domains, and the display appears whitish caused by the scattering of light.
FIG. 1a is a conventional PDLC glass window 100 in an off state. Two glass substrates 102a, 102b are provided. A conductive coating 104 is applied to the inner surface of the outer substrate 102a (e.g., surface 2 of the window assembly). A plurality of liquid crystal (LC) droplets 108 are disposed within the polymer mixture 106. Because no voltage is provided, the droplets 108 are randomly oriented, and incident light I reflects off of them, causing the scattering of light in the directions shown by the dashed arrows.
In the addressed state, the nematic texture in different domains align with the electric field, thus allowing for a clear state. FIG. 1b is a conventional PDLC glass window 100 in an on state. FIG. 1b is similar to FIG. 1a, except that a voltage V is applied to the PDLC layer (e.g., to the conductive coating 104) via one or more bus bars (not shown). The voltage causes the liquid crystal droplets to align parallel to the electric field, allowing incident light I to pass through the window 100 in the clear state.
Popular uses of this technology include glass walls in offices, conference rooms, lobbies, store fronts, etc. Privacy glass sometimes is used by homeowners (e.g., in bathrooms, entryways, family rooms, bedrooms, skylights, etc.). The windows may be made to function on a standard voltage and may be connected to switches. Windows also may be connected to timers.
Unfortunately, although such techniques have represented an improvement in some windows, there still are certain drawbacks. Although the electric field dramatically reduces the scattering, there still exists scattering at the boundary of the liquid crystal and polymer, and scattering between neighboring drops. This contributes in part to a residual haze in the clear state. Another contribution to the residual haze in the clear state relates to the polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA) used to laminate the PDLC to the glass.
Furthermore, as another example drawback of current PDLC techniques, such windows suffer from UV and solar-induced degradation of the PDLC layer, ultimately causing color change and/or flicker. As used herein, “UV” refers to light having a wavelength less than or equal to about 400 nm. More particularly, long-term exposure of the cured and laminated PDLC to ambient UV light exacerbates the haze values and causes a “browning” of the LC (although such values are material dependent, after about 3,000 hours of UV exposure, generally ΔE*>2, with ΔE* being known as a value indicative of color and transmission change of light, where ΔE*=sqrt((ΔL*)2+(Δa*)2+(Δb*)2), with L* corresponding to the “lightness” of the color, a* corresponding to the color's position between red and green, and b* corresponding to the color's position between blue and yellow). Even though the PVB layer cuts off about 99% of the UV radiation below about 380 nm, a large portion of UVA (e.g., having a penetration depth of long wavelength UVA in the order of magnitude of PVB thickness) may still cause structural changes in both the polymer as well as the LC, making determining the size of the droplets, and hence the scattering function, difficult and susceptible to change. As used herein, “UVA” refers to light having a wavelength from about 320 nm to about 400 nm. The UV also may degrade and/or fade the colored PVB layers. This susceptibility to degradation and/or fading is true for dye-based PVB, as well as in pigment-based PVB.
The degradation is exacerbated with temperature increases in the LCs. Because the thermal conductivity of the PVB, PET, and/or LC is low, radiation causes thermal runaways if samples are left exposed to the sun for relatively long periods of time.
Another degradation of PDLC performance relates to the switching times of the LC as its exposure to UV and heat increases. Response time essentially is a function of the sum of the time on and time off (Ton+Toff). Initially, the response time of the device is just under about 20 ms, which corresponds to a frequency of about 100 Hz. This frequency is well above 25 Hz, which is generally regarded as the frequency at which the human eye can perceive flicker. However, after about 1,000 hours of QUV accelerated weathering, the response time may climb above about 40 ms, which may make flicker noticeable to the human eye.
Still another set of problems relates to delamination. Currently, curved laminates with sharp edges are susceptible to delamination in and/or proximate to high-stress hot-spots.
Thus, it will be appreciated that there is a need in the art for coated articles that overcome one or more of these and/or other disadvantages. It also will be appreciated that there is a need in the art for improved PDLC techniques (for use in, for example, vehicle windows, insulating glass (IG) window units, etc.).
In certain example embodiments of this invention, there is provided a window (e.g., vehicle windshield, architectural window, or the like) comprising: an inner substrate and an outer substrate, the inner and outer substrates being substantially parallel to one another; a multi-layer low-E ultraviolet (UV) blocking coating supported by an inner surface of the outer substrate, the low-E UV blocking coating blocking significant amounts of UV in the range of from about 380-400 nm; a liquid crystal inclusive layer disposed between at least the inner and outer substrates; first and second substantially transparent conductive layers, the first and second substantially transparent conductive layers being provided between the liquid crystal inclusive layer and the outer and inner substrates, respectively; first and second polymer inclusive laminating layers, the first laminating layer provided between at least the liquid crystal inclusive layer and the outer substrate and the second laminating layer provided between at least the liquid crystal inclusive layer and the inner substrate; at least one bus bar in electrical communication with the first and/or second transparent conductive layer(s) so as to cause the liquid crystal inclusive layer to become activated when a voltage is applied thereto; and wherein the multi-layer low-E UV blocking coating comprises at least one IR reflecting layer and at least one UV blocking layer so that no more than about 20% of ambient light having a wavelength of from 380-400 nm reaches the liquid crystal inclusive layer, and wherein the coated article has a visible transmission of at least about 55% when the liquid crystal inclusive layer is activated.
In certain example embodiments of this invention, there is provided a coated article including a low-E coating supported by a substrate, the low-E coating comprising: first and second IR reflecting layers comprising silver and/or gold; at least one UV blocking layer that blocks significant amounts of UV light having a wavelength of from 380-400 nm so that no more than about 20% of light having a wavelength of from 380-400 passes through the low-E coating; and wherein the UV blocking layer is positioned so as to not directly contact the first and second IR reflecting layers. This coated article may be used in a window unit or the like in different example embodiments of this invention, and the substrate may be based on glass in certain example instances.
In certain example embodiments of this invention, a coated article and/or a method of making the same is/are provided. An inner substrate and an outer substrate are provided. The inner and outer substrates are substantially parallel to one another. A multi-layer low-E UV blocking coating is supported by an inner surface of the outer substrate. A liquid crystal inclusive layer is disposed between the inner and outer substrates. First and second transparent conductive layers are provided. The first and second transparent conductive layers are provided between the liquid crystal inclusive layer and the outer and inner substrates, respectively. First and second laminate layers are provided. The first laminate layer is for lamination to the outer substrate, and the second laminate layer is for lamination to the inner substrate. At least one bus bar is operably connected to the liquid crystal inclusive layer through the first and/or second transparent conductive layer(s) so as to cause the liquid crystal inclusive layer to become activated when a voltage is applied to the at least one bus bar. The multi-layer low-E UV blocking coating is arranged so that no more than about 20% of light having a wavelength of about 380-400 nm reaches the liquid crystal inclusive layer. The coated article has a visible transmission of from about 55-65% when the liquid crystal inclusive layer is activated.
In certain example embodiments of this invention, an insulating glass unit and/or a method of making the same is/are provided. Three substantially parallel substrates are provided. A multi-layer low-E UV blocking coating is supported by a surface of the second substrate facing the third substrate. A liquid crystal inclusive layer is disposed between the second and third substrates. First and second transparent conductive layers are provided. The first and second transparent conductive layers are provided between the liquid crystal inclusive layer and the second and third substrates, respectively. First and second laminate layers are provided. The first laminate layer is for lamination to the second substrate and the second laminate layer is for lamination to the third substrate. At least one bus bar is operably connected to the liquid crystal inclusive layer through the first and/or second transparent conductive layer(s) so as to cause the liquid crystal inclusive layer to become activated when a voltage is applied to the at least one bus bar. The first and second substrates are spaced apart. The multi-layer low-E UV blocking coating is arranged so that no more than about 20% of light having a wavelength of about 380-400 nm reaches the liquid crystal inclusive layer. The insulating glass unit has a visible transmission of from about 55-65% when the liquid crystal inclusive layer is activated.
In certain example embodiments of this invention, a coated article including a low-E UV blocking coating supported by a substrate and/or a method of making the same is/are provided. The low-E UV blocking coating comprises first and second IR reflecting layers comprising silver and/or gold, and a UV blocking layer that blocks light having a wavelength of about 380-400 nm so that no more than about 20% of such light penetrates the coating. The coated article has a visible transmission of at least about 55%.
In certain example embodiments of this invention, an insulating glass (IG) unit including a low-E UV blocking coating supported by a substrate and/or a method of making the same is/are provided. The low-E UV blocking coating comprises first and second IR reflecting layers comprising silver and/or gold, and a UV blocking layer that blocks light having a wavelength of about 380-400 nm so that no more than about 20% of such light penetrates the coating. The IG unit has a visible transmission of at least about 55%.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.